An apparatus of the afore-mentioned kind is used for the endoscopic irrigation of body cavities, for example the bladder, the uterus or articular capsules.
The apparatus known from the afore-mentioned document U.S. Pat. No. 4,902,277 can be specially used in arthroscopy in an endoscopic resection of a joint. In this connection, a physiological liquid is pumped by means of an irrigation pump through an irrigation conduit into the joint. The liquid is then drawn off from the joint by means of a suction pump through a suction conduit.
It is desirable during such an endoscopic irrigation of hollow organs that the pressure and the flow rate of the irrigation liquid in the body cavity can be adjusted independently from one another. The flow rate is to be understood as the liquid debit through the body cavity per time unit.
The irrigation pump of the afore-mentioned known apparatus is a displacement pump, which is controlled as a function of the actual pressure in the irrigation conduit or in the body cavity, which is measured by a pressure sensor, in order to maintain a predetermined nominal pressure in the body cavity. The speed of the motor of the irrigation pump is increased or reduced as a function of the actual pressure measured by the pressure sensor, in order to maintain the nominal pressure in the body cavity.
The suction pump of this known apparatus is a displacement pump, too, which is controlled as a function of a predetermined nominal flow rate. In this connection, two flow rates can be adjusted, as a function of which the suction pump is controlled. The suction pump maintains the predetermined flow rate which has been set respectively. The higher nominal flow rate can be set, for example, when a working instrument, for example a resection instrument, is additionally put into operation. The lower nominal flow rate can be set, for example, when the body cavity is just to be irrigated without a working instrument being in operation.
The use of a displacement pump, in particular a roller pump, has the advantage that the flow rate produced by the pump is, to a high degree, proportional to the speed of the displacement pump in particular if the pressure maintained by the irrigation pump is constant.
A disadvantage of this known apparatus comes to light when an obstruction which is, for example, caused by tissue pieces, occurs in the suction conduit. In case of an obstruction in the suction conduit, the actual pressure in the body cavity exceeds the nominal pressure with the result that the irrigation pump of the known apparatus is controlled such that its speed decreases, in order to maintain the nominal pressure. In contrast to that, the suction pump which is adjusted to the predetermined nominal flow rate, works on with an unchanged speed. The result is that the obstruction possibly cannot be drawn off by the suction pump. This can lead to a disturbance and interruption of the irrigation operation and, thereby, of the medical operation.
On the other hand, an apparatus for irrigating a body cavity is known from EP 0 529 902 A2, the irrigation pump of which is a centrifugal pump, which is controlled as a function of a predetermined nominal pressure in the body cavity or in the irrigation conduit, respectively, while the suction pump is a displacement pump in form of a gear pump. Unlike a displacement pump, a centrifugal pump has the characteristic that the produced flow rate is not a single-valued function of the speed of the centrifugal pump, but in addition depends on the actual pressure. With this known apparatus, the flow rate is adjusted by means of a controllable tube-squeezing valve.
This known apparatus has the disadvantage that the irrigation pump, which is designed as a centrifugal pump, is not sealing so that in case that the squeezing valve is not closed and both pumps are not activated, the liquid can unimpededly flow through as a result of the gradient. Another disadvantage of this known apparatus is, as mentioned before, that by using a centrifugal pump as the irrigation pump, the flow rate cannot be preset in exact manner because neither the irrigation pump nor the suction pump allow a simple dependency of the flow rate for example as a function of the speed of the pumps. In this known apparatus, the actual flow rate highly depends on the pressure difference in the system.
It is an object of the invention to provide an apparatus of the afore-mentioned kind by means of which the pressure and the flow rate can be controlled as independently from each other as possible and in a way which differs from the known apparatus.